The basis of this sci-fi story, set in 2085, but constantly brought to a jarring halt by flashbacks to previous time periods is that of a medical compound which was developed experimentally which could reverse aging. The details of how this was supposed to work the way it did were kept vague, with some hand-waving at telomeres which are genetic components that seem somehow, to be connected with cell aging and death. I really don't expect a sci-fi writer to explain the details of something they invent, or the science underlying it. I prefer it if they vaguely wave their hand at quantum this, or wormhole that, or at "Vita-Rays"! I'm good with that 'explanation' for the sake of a good story, but if you're going to posit something, then for me you need to be consistent about it, and it needs to make some sort of sense within its framework. This author failed for me in this regard.
In the year 2000, Anny Beth and Melly were very old and not so far from death when they were offered the chance to try a series of injections which would literally reverse their aging, by doctors Jimson and Reed. Jimson Reed? Seriously? When they reached an age they were comfortable with, they would have their medication balanced so that they were maintained at that age indefinitely. There were problems with this, the first of which is that for each year they reversed their age, they would lose a year of their memories. How this worked went unexplained and made no sense. The real problem though, came when they first tried to apply the 'arresting' technique to a volunteer. He died horribly - in a way similar to that in which some vampires die: they rapidly wither and turn to dust. It was silly at best.
Given this death threat, the others were not offered the arresting shots and so continued to "unage" as the author puts it. A better term is that they continued to youth! I think so, anyway. So when we meet our two girls they are literally girls, of sixteen and eighteen, and their future is going to be them 'youthing' all the way back to the moment of their birth, when they will die. Again, how that works is unexplained. Note that the book blurb simply lies when it says, " They have no idea what will happen when they hit age zero." According to the author, who presumably didn't write the blurb, they do know.
The two have chosen to live outside of the community of fellow experimentees, but they're reaching an age when they will need a guardian because they cannot be legally in charge of themselves. When they discover that a reporter is trying to track them down, they go on the run. At that point I knew exactly how it would end, and it ended almost exactly how I had envisioned it, so there really isn't much surprise here. If I can figure it out, anyone can! I'd thought that perhaps they would get cured and start to age (or in their case, re-age) naturally with the guardian they found, but this didn't happen.
The ending was not great, predictable as it was, so it was one more disappointment in a disappointing book and rather reminiscent of the Star Trek episode which has the crew meeting an alien race which lives its life backwards, being "born" as adults (how that worked went unexplained!) and dying as children. That story made no sense either! I cannot recommend this because of the poor writing and wasted potential.